U.S. patent application number 09/963395 was filed with the patent office on 2002-04-04 for hydraulic brake system for vehicle.
Invention is credited to Nishii, Michiharu, Nitta, Hirofumi, Oishi, Masaki, Terazawa, Tadashi.
Application Number | 20020038977 09/963395 |
Document ID | / |
Family ID | 18777706 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020038977 |
Kind Code |
A1 |
Nitta, Hirofumi ; et
al. |
April 4, 2002 |
Hydraulic brake system for vehicle
Abstract
A vehicle hydraulic brake system includes a hydraulic pressure
generator which pressurizes brake fluid supplied from a reservoir
to apply brake pressure to a wheel cylinder in response to
operation of a brake member, an auxiliary hydraulic pressure source
having an accumulator and a hydraulic pump that pressurizes brake
fluid supplied from the reservoir to a predetermined level for
generating power hydraulic pressure, and an output hydraulic
pressure detector for continuously detecting an output hydraulic
pressure of the accumulator. A vehicle condition detector
continuously detects an operating condition of the vehicle and a
driving condition setting device sets a driving condition of the
hydraulic pump based on the detected operating condition of the
vehicle. A driving control device controls the hydraulic pump based
on the driving condition of the hydraulic pump set by the driving
condition setting device and the output hydraulic pressure of the
accumulator.
Inventors: |
Nitta, Hirofumi; (Obu-shi,
JP) ; Nishii, Michiharu; (Toyota-shi, JP) ;
Terazawa, Tadashi; (Toyota-shi, JP) ; Oishi,
Masaki; (Toyota-shi, JP) |
Correspondence
Address: |
Platon N. Mandros, Esquire
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
18777706 |
Appl. No.: |
09/963395 |
Filed: |
September 27, 2001 |
Current U.S.
Class: |
303/138 |
Current CPC
Class: |
B60T 13/148 20130101;
B60T 8/4845 20130101; B60T 17/18 20130101; B60T 8/4054 20130101;
B60T 8/3275 20130101 |
Class at
Publication: |
303/138 |
International
Class: |
B60T 008/32 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2000 |
JP |
2000-295250 |
Claims
What is claimed is:
1. A hydraulic brake system for a vehicle comprising: a hydraulic
pressure generating device for pressurizing brake fluid supplied
from a reservoir to apply a brake pressure to a wheel cylinder in
response to operation of a brake operating member; an auxiliary
hydraulic pressure source having an accumulator and a hydraulic
pump, the hydraulic pump pressurizing the brake fluid supplied from
the reservoir to a predetermined level for generating a power
hydraulic pressure; an output hydraulic pressure detecting means
for continuously detecting an output hydraulic pressure of the
accumulator of the auxiliary hydraulic pressure source; vehicle
condition detecting means for continuously detecting an operating
condition of the vehicle; driving condition setting means for
setting a driving condition of the hydraulic pump based on the
operating condition of the vehicle detected by the vehicle
condition detecting means; and driving control means for
controlling the hydraulic pump based on the driving condition of
the hydraulic pump set by the driving condition setting means and
the output hydraulic pressure of the accumulator of the auxiliary
hydraulic pressure source.
2. The hydraulic brake system for a vehicle in accordance with
claim 1, wherein the driving condition setting means includes a
vehicle stop judging means for judging whether or not the vehicle
is stopped, the driving condition setting means setting the driving
condition of the hydraulic pump so that the output hydraulic
pressure of the auxiliary hydraulic pressure source is smaller when
the stop judging means judges that the vehicle is stopped than the
output hydraulic pressure when the stop judging means judges that
the vehicle is running.
3. The hydraulic brake system for a vehicle in accordance with
claim 1, wherein the vehicle condition detecting means includes an
operation amount detecting means for detecting an operating amount
of the brake operating member and deceleration detecting means for
detecting a deceleration of the vehicle, the driving condition
setting means judging occurrence of brake fade based on the
operating amount detected by the operation amount detecting means
and the deceleration detected by the deceleration detecting means,
and the driving condition setting means setting the driving
condition of the hydraulic pump so that the output hydraulic
pressure of the auxiliary hydraulic pressure source is larger when
the driving condition setting means judges the occurrence of brake
fade than the output hydraulic pressure under normal braking
operation.
4. The hydraulic brake system for a vehicle in accordance with
claim 1, wherein the hydraulic pressure generating device includes
a master cylinder and a hydraulic booster assisting operation of
the master cylinder by using the power hydraulic pressure generated
by the auxiliary hydraulic pressure source.
5. The hydraulic brake system for a vehicle in accordance with
claim 1, wherein the output hydraulic pressure detecting means
includes a first pressure sensor for detecting the hydraulic
pressure of the auxiliary hydraulic pressure source.
6. The hydraulic brake system for a vehicle in accordance with
claim 1, wherein the vehicle condition detecting means includes at
least one of a wheel sensor detecting a wheel speed of the vehicle,
a stroke sensor detecting a stroke amount of the brake operating
member, a vehicle height sensor detecting a height of the vehicle,
and a second pressure sensor detecting the brake pressure generated
by the hydraulic pressure generating device.
7. The hydraulic brake system for a vehicle in accordance with
Claim 2, wherein the vehicle condition detecting means includes an
operation amount detecting means for detecting an operating amount
of the brake operating member and deceleration detecting means for
detecting a deceleration of the vehicle, the driving condition
setting means judging an occurrence of brake fade based on the
operating amount detected by the brake operation amount detecting
means and the deceleration detected by the deceleration detecting
means, and the driving condition setting means setting the driving
condition of the hydraulic pump so that the output hydraulic
pressure of the auxiliary hydraulic pressure source is larger when
the driving condition setting means judges the occurrence of brake
fade than the output hydraulic pressure under normal braking
operation.
8. The hydraulic brake system for a vehicle in accordance with
claim 1, wherein the auxiliary hydraulic pressure source further
includes an electric motor for driving the hydraulic pump and the
accumulator is connected at an output side of the hydraulic
pump.
9. A hydraulic brake system for a vehicle comprising: a hydraulic
pressure generating device for pressurizing brake fluid supplied
from a reservoir to apply a brake pressure to a wheel cylinder in
response to operation of a brake operating member; an auxiliary
hydraulic pressure source having an accumulator and a hydraulic
pump, the hydraulic pump pressurizing the brake fluid supplied from
the reservoir to a predetermined level for generating a power
hydraulic pressure; an output hydraulic pressure detecting means
for continuously detecting an output hydraulic pressure of the
accumulator of the auxiliary hydraulic pressure source; vehicle
condition detecting means for continuously detecting at least one
of a plurality of operating conditions of the vehicle, including
whether the vehicle is in a stopped condition or a running
condition, whether a vehicle load is greater than or less than a
predetermined value, the absence or presence of an automatic
braking condition, the absence or presence of a sudden breaking
condition, and the absence or presence of a brake fade occurrence;
driving condition setting means which sets a first driving
condition of the hydraulic pump when the vehicle condition
detecting means detects at least one of the stopped condition of
the vehicle, the vehicle load being less than the predetermined
value, the absence of the automatic braking condition, the absence
of the sudden breaking condition and the absence of brake fade
occurrence, and sets a second driving condition higher than the
first driving condition when the vehicle condition detecting means
detects at least one of the running condition of the vehicle, the
vehicle load being greater than the predetermined value, the
presence of the automatic braking condition, the presence of the
sudden breaking condition and the presence of brake fade
occurrence; and driving control means for controlling the hydraulic
pump based on either the first or second driving condition set by
the driving condition setting means and the output hydraulic
pressure of the accumulator of the auxiliary hydraulic pressure
source.
10. The hydraulic brake system for a vehicle in accordance with
claim 9, wherein the vehicle condition detecting means includes an
operation amount detecting means for detecting an operating amount
of the brake operating member and deceleration detecting means for
detecting a deceleration of the vehicle, the driving condition
setting means judging the presence brake fade occurrence based on
the operating amount detected by the operation amount detecting
means and the deceleration detected by the deceleration detecting
means.
11. The hydraulic brake system for a vehicle in accordance with
claim 9, wherein the hydraulic pressure generating device includes
a master cylinder and a hydraulic booster assisting operation of
the master cylinder by using the power hydraulic pressure generated
by the auxiliary hydraulic pressure source.
12. The hydraulic brake system for a vehicle in accordance with
claim 9, wherein the output hydraulic pressure detecting means
includes a first pressure sensor for detecting the hydraulic
pressure of the auxiliary hydraulic pressure source.
13. The hydraulic brake system for a vehicle in accordance with
claim 9, wherein the vehicle condition detecting means includes at
least one of a wheel sensor detecting a wheel speed of the vehicle,
a stroke sensor detecting a stroke amount of the brake operating
member, a vehicle height sensor detecting a height of the vehicle,
and a second pressure sensor detecting the brake pressure generated
by the hydraulic pressure generating device.
14. The hydraulic brake system for a vehicle in accordance with
claim 9, wherein the auxiliary hydraulic pressure source further
includes an electric motor for driving the hydraulic pump and the
accumulator is connected at an output side of the hydraulic pump.
Description
FIELD OF THE INVENTION
[0001] The present invention is generally related to a hydraulic
brake system for a vehicle. More specially, the present invention
pertains to a vehicle hydraulic brake system having, in addition to
a hydraulic pressure source which supplies hydraulic pressure in
response to brake operation, an auxiliary hydraulic pressure source
pressurizing brake fluid through use of a hydraulic pump.
BACKGROUND OF THE INVENTION
[0002] One known type of hydraulic brake system includes a master
cylinder serving as a hydraulic pressure generator for supplying
hydraulic pressure in response to brake operation and an auxiliary
hydraulic pressure source including a hydraulic pump and an
accumulator. In this hydraulic brake system, it is necessary to
control the hydraulic pressure outputted from the auxiliary
hydraulic pressure source. In addition, it is necessary to issue a
warning when the hydraulic pressure drops.
[0003] U.S. Pat. No. 5,000,520 discloses a hydraulic brake system.
In its discussion of the operation of other known hydraulic brake
systems, the patent states that the auxiliary pressure can vary
within given limits of, for example, within 140 to 180 bar. The
patent also describes that in these systems, the hydraulic pump is
switched on as soon as the auxiliary pressure drops to the lower
limit and remains in operation until the upper limit is reached.
If, due to a defect for example, the auxiliary pressure drops below
the lower limit and reaches an auxiliary pressure minimum set at
105 bar, the patent states that a warning signal is produced.
[0004] U.S. Pat. No. 5,000,520 proposes a switching arrangement for
controlling the hydraulic pump of an auxiliary pressure supply
system in which a switching contact of a motor relay turns on or
off an electric motor that drives the hydraulic pump. When the
switching contact of the motor relay is defective, a sole pressure
switch and sole switching relay are provided to maintain the output
hydraulic pressure of the auxiliary hydraulic pressure source
within a predetermined pressure range, to issue the warning signal
by another pressure switch when the accumulator pressure drops
below its lower limit, and to drive the motor by another switching
relay.
[0005] According to the system described in U.S. Pat. No.
5,000,520, the hydraulic pump can operate even if the accumulator
pressure drops, and so it is possible to maintain the driving state
of the hydraulic pump. However, maintaining the accumulator
pressure within the pressure range by the sole pressure switch may
result in the accumulator pressure being maintained at a higher
pressure level than the desired pressure level, thus causing
wasteful consumption of the energy for driving the hydraulic pump.
In addition, to cope with the sole pressure switch operation, the
capacity of the accumulator has to be made sufficient, resulting in
the need for a larger accumulator.
[0006] A need thus exists for a hydraulic brake system that is not
as susceptible to the same disadvantages and drawbacks mentioned
above.
SUMMARY OF THE INVENTION
[0007] In accordance with one aspect of the present invention, a
hydraulic brake system for a vehicle includes a hydraulic pressure
generating device for pressurizing brake fluid supplied from a
reservoir to apply a brake pressure to a wheel cylinder in response
to operation of a brake operating member, an auxiliary hydraulic
pressure source having an accumulator and a hydraulic pump that
pressurizes the brake fluid supplied from the reservoir to a
predetermined level for generating a power hydraulic pressure, and
an output hydraulic pressure detecting device for continuously
detecting an output hydraulic pressure of the accumulator of the
auxiliary hydraulic pressure source. A vehicle condition detecting
device continuously detects an operating condition of the vehicle,
a driving condition setting device sets a driving condition of the
hydraulic pump based on the operating condition of the vehicle
detected by the vehicle condition detecting device, and a driving
control device controls the hydraulic pump based on the driving
condition of the hydraulic pump set by the driving condition
setting device and the output hydraulic pressure of the accumulator
of the auxiliary hydraulic pressure source.
[0008] The hydraulic brake system thus continuously observes the
power hydraulic pressure outputted by the auxiliary hydraulic
pressure source and also continuously observes the operating
condition of the vehicle, and then sets the driving condition of
the hydraulic pump based on the operating condition. The hydraulic
brake system is thus constructed to control the operation of the
hydraulic pump based on the driving condition and the power
hydraulic pressure. Accordingly, the hydraulic brake system can
appropriately control the hydraulic pump, whereby the hydraulic
brake system obtains or provides a good brake feel. Additionally,
energy efficiency and durability of the hydraulic pump are
improved.
[0009] The driving condition setting device includes a stop judging
mechanism for judging whether or not the vehicle is stopping, and
sets the driving condition of the hydraulic pump so that the output
hydraulic pressure of the auxiliary hydraulic pressure source is
smaller when the stop judging mechanism judges that the vehicle is
stopped than the output hydraulic pressure when the stop judging
mechanism judges that the vehicle is running. When the vehicle is
judged to be stopped, the vehicle hydraulic brake system sets the
driving condition for the hydraulic pump to generate a lower power
hydraulic pressure compared to the power hydraulic pressure when
the vehicle is judged to be running. Accordingly, the noise of the
hydraulic pump is reduced, while at the same time improving the
energy efficiency and durability of the hydraulic pump.
[0010] The vehicle condition detecting device includes a brake
operation amount detecting mechanism for detecting the operating
amount of the brake operating member and a deceleration detecting
mechanism for detecting a deceleration of the vehicle. The driving
condition setting device judges whether or not a brake fade occurs
based on the operating amount detected by the brake operation
amount detecting mechanism and the deceleration detected by the
deceleration detecting mechanism. The driving condition setting
device sets the driving condition of the hydraulic pump so that the
output hydraulic pressure of the auxiliary hydraulic pressure
source is larger when the driving condition setting device judges
that brake fade occurs than the output hydraulic pressure under
normal braking operation.
[0011] The vehicle hydraulic brake system thus judges whether or
not the brake fade occurs based on the operating amount of the
brake operating member and the deceleration of the vehicle body.
When the hydraulic brake system judges the occurrence of brake
fade, the driving condition for the hydraulic pump is set in order
that the auxiliary hydraulic pressure source outputs the power
hydraulic high. Accordingly, the hydraulic brake system is able to
appropriately control the hydraulic pump. Also, the hydraulic brake
system is able to produce the required braking force even if brake
fade occurs.
[0012] The hydraulic pressure generating device includes a master
cylinder and a hydraulic booster that assists the operation of the
master cylinder by using the power hydraulic pressure generated by
the auxiliary hydraulic pressure source. The output hydraulic
pressure detecting device includes a first pressure sensor for
detecting the hydraulic pressure of the auxiliary hydraulic
pressure source.
[0013] The vehicle condition detecting device includes at least one
of a wheel sensor detecting a wheel speed of the vehicle, a stroke
sensor detecting a stroke amount of the brake operating member, a
vehicle height sensor detecting a height of the vehicle, and a
second pressure sensor detecting the brake pressure generated by
the hydraulic pressure generating device.
[0014] The driving condition setting device includes a stop judging
mechanism for judging whether or not the vehicle is stopped. The
driving condition setting device then sets the driving condition of
the hydraulic pump so that the output hydraulic pressure of the
auxiliary hydraulic pressure source is smaller when the stop
judging mechanism judges that the vehicle is stopped than the
output hydraulic pressure when the stop judging mechanism judges
that the vehicle is running. The vehicle condition detecting device
also includes a brake operation amount detecting mechanism for
detecting an operating amount of the brake operating member and a
deceleration detecting mechanism for detecting the deceleration of
the vehicle. The driving condition setting device judges whether or
not a brake fade occurs based on the operating amount detected by
the brake operation amount detecting mechanism and the deceleration
detected by the deceleration detecting mechanism, with the driving
condition setting device setting the driving condition of the
hydraulic pump so that the output hydraulic pressure of the
auxiliary hydraulic pressure source becomes larger when the driving
condition setting device judges that brake fade occurs than the
output hydraulic pressure under normal braking operation.
[0015] The auxiliary hydraulic pressure source also includes an
electric motor for driving the hydraulic pump, with the accumulator
being connected at an output side of the hydraulic pump.
[0016] In accordance with another aspect of the invention, a
hydraulic brake system for a vehicle includes a hydraulic pressure
generating device which generates pressurizing brake fluid supplied
from a reservoir to apply a brake pressure to a wheel cylinder in
response to operation of a brake operating member, an auxiliary
hydraulic pressure source having an accumulator and a hydraulic
pump that pressurizes the brake fluid supplied from the reservoir
to a predetermined level for generating a power hydraulic pressure,
and an output hydraulic pressure detector for continuously
detecting an output hydraulic pressure of the accumulator of the
auxiliary hydraulic pressure source. A vehicle condition detector
continuously detects at least one of a plurality of operating
conditions of the vehicle, including whether the vehicle is in a
stopped condition or a running condition, whether a vehicle load is
greater than or less than a predetermined value, the absence or
presence of an automatic braking condition, the absence or presence
of a sudden breaking condition, and the absence or presence of a
brake fade occurrence. A driving condition setting device sets a
first driving condition of the hydraulic pump when the vehicle
condition detector detects at least one of the stopped condition of
the vehicle, the vehicle load being less than the predetermined
value, the absence of the automatic braking condition, the absence
of the sudden breaking condition and the absence of brake fade
occurrence, and sets a second driving condition higher than the
first driving condition when the vehicle condition detector detects
at least one of the running condition of the vehicle, the vehicle
load being greater than the predetermined value, the presence of
the automatic braking condition, the presence of the sudden
breaking condition and the presence of brake fade occurrence. A
driving controller controls the hydraulic pump based on either the
first or second driving condition set by the driving condition
setting device and the output hydraulic pressure of the accumulator
of the auxiliary hydraulic pressure source.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0017] The foregoing and additional features and characteristics of
the present invention will become more apparent from the following
detailed description considered with reference to the accompanying
drawing figures in which like reference numerals designate like
elements.
[0018] FIG. 1 is a schematic block diagram of a hydraulic brake
system in accordance with the present invention.
[0019] FIG. 2 is a graph showing limit values for the control
operation of accumulator hydraulic pressure in accordance with the
present invention.
[0020] FIG. 3 shows a schematic block diagram of an electronic
control device used in the present invention.
[0021] FIG. 4 shows a flowchart of the driving control operation of
the hydraulic pump in accordance with the present invention.
[0022] FIG. 5 is a graph showing the relationship between the
hydraulic pressure of a master cylinder and braking force of a
general hydraulic brake system.
[0023] FIG. 6 is a graph showing the relationship between the
hydraulic pressure of a master cylinder and the braking force
employed in the judgment of a brake fade.
[0024] FIG. 7 is a graph showing the limit values for another
control operation of accumulator hydraulic pressure in accordance
with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring initially to FIG. 1 which schematically
illustrates the structure of the hydraulic brake system according
to the present invention, the hydraulic brake control device
includes a pressure generator PG and an auxiliary hydraulic
pressure source AP. The pressure generator PG pressurizes brake
fluid supplied from a reservoir RV in response to operation of a
brake pedal BP which acts as a brake operating member, and outputs
hydraulic pressure as pressurized brake fluid. The auxiliary
hydraulic pressure source AP increases the pressure of the brake
fluid supplied from the reservoir RV to a predetermined level by
driving a hydraulic pump FP, and outputs a power hydraulic
pressure. The hydraulic pump FP, which constitutes the auxiliary
hydraulic pressure source AP or a part of the auxiliary hydraulic
pressure source AP, is driven by an electric motor M. The hydraulic
pump FP has an inlet side connected with the reservoir RV and an
outlet side connected with an accumulator AC by way of a
check-valve CV.
[0026] The accumulator AC is connected with a pressure sensor PS1
forming an output hydraulic pressure detecting means for
continuously detecting an accumulator hydraulic pressure, i.e., the
hydraulic pressure of the accumulator AC or the hydraulic pressure
outputted from the auxiliary hydraulic pressure source AP. The
hydraulic pump FP is controlled by a driving control means FC based
on the hydraulic pressure detected by the pressure sensor PS1 and a
driving condition set by a driving condition setting means DC which
will be described in more detail below.
[0027] As shown in FIG. 2, the electric motor M is controlled to
start when the accumulator hydraulic pressure reaches or becomes a
lower limit Pn, and is further controlled to stop when the
accumulator hydraulic pressure becomes or reaches an upper limit
Pf. Between the lower limit and the upper limit, three pressure
ranges A, B, C are defined, in order that the accumulator hydraulic
pressure is set to be within any one of the three pressure ranges,
with the driving control means FC controlling the electric motor M
and further the hydraulic pump FP based on the driving condition
set by the driving condition setting means DC. The bold solid line
in FIG. 2 indicates an example of the relationship between a stored
amount of the brake fluid in the accumulator AC and the accumulator
hydraulic pressure when the auxiliary hydraulic pressure source AP
is driven. In addition, the reference character Pw shown in FIG. 2
indicates a minimum standard hydraulic pressure (Pw<Pn). If the
accumulator hydraulic pressure is less than the minimum standard
hydraulic pressure, a warning is issued.
[0028] The pressure range A shown in FIG. 2 ranges from the lower
limit Pn to a set pressure PfA, the pressure range B ranges from
the set pressure PfA to the upper limit Pf, and the pressure range
C ranges from the lower limit Pn to a set pressure PfC. The set
pressure PfA is a pressure less than the upper limit pressure Pf
and beyond or greater than the lower limit pressure Pn. The set
pressure PfC is a pressure greater than the lower limit Pn and
lower than the set pressure PfA.
[0029] It is to be understood that the pressure ranges of the
accumulator hydraulic pressure can alternatively be set as the
pressure ranges shown in FIG. 7. Here, the pressure ranges A and C
are identical with the pressure ranges A and C in FIG. 2,
respectively. The pressure range B ranges from the lower limit Pn
to the set pressure PfB. The set pressure PfB is a pressure higher
than or greater than the set pressure PfA.
[0030] Referring once again to FIG. 1, the vehicle condition
detecting means is provided with a wheel speed sensor WS detecting
a wheel speed, a pedal stroke sensor BS detecting the stroke as the
operational amount of the brake pedal which acts as the brake
operation member, a vehicle height sensor HS detecting the height
of the vehicle body relative to the road surface, and a pressure
sensor PS2 detecting the hydraulic pressure outputted by the
pressure generator PG. Of course, the vehicle condition detecting
means is not limited to these sensors, and can include one or more
other sensors.
[0031] The driving condition setting means DC is designed to judge
whether or not the vehicle is stopped based on the wheel speed
detected by the wheel speed sensor WS. If it is determined that the
vehicle is stopped (i.e., the vehicle engine is operating, but the
vehicle is stopped), the driving conditions of the hydraulic pump
FP is set in order that the hydraulic pressure outputted from the
auxiliary hydraulic pressure source AP (i.e., the accumulator
hydraulic pressure) is set to be lower than that when it is
determined that the vehicle is running. More specifically, if the
vehicle is found to be running, the drive starting timing and the
drive terminating timing of the hydraulic pump FP are set in order
that the accumulator hydraulic pressure becomes within the pressure
range A in FIG. 2. In other words, the drive starting timing is set
when the accumulator hydraulic pressure exceeds the lower limit Pn,
while the drive terminating timing is set when the accumulator
hydraulic pressure reaches the set pressure PfA. On the other hand,
while the vehicle is stopped, both the drive starting timing and
the drive terminating timing of the electric motor M are set in
order that the accumulator hydraulic pressure is within the
pressure range C. That is, the driving starting timing is set when
the accumulator hydraulic pressure exceeds the lower limit Pn (like
when the vehicle is normally running), while the drive terminating
timing is set when the accumulator hydraulic pressure reaches the
set pressure PfC.
[0032] It is noted that in the described and illustrated
embodiment, the driving current (driving duty) of the electric
motor is set to the maximum (100%). However, for reducing noise
while the electric motor M is driven, the driving current (driving
duty) of the electric motor can be set to less than the maximum.
The driving current (the driving duty) of the electric motor M can
be set to the maximum (100%) for improving the responsiveness while
the vehicle is running and can be smaller than the maximum while
the vehicle is stopped.
[0033] In addition, according to the driving condition setting
means DC of the present embodiment, the weight of the load on the
vehicle (i.e., a vehicle load) is determined based on the output
signal from the vehicle height sensor HS. If the vehicle load is
found to be large, the diving condition of the hydraulic pump FP is
set for making the accumulator hydraulic pressure larger than that
when the vehicle load is small, whereby the drive starting and
terminating timings are set in order that the accumulator hydraulic
pressure is within the pressure range B. Moreover, a determination
is made of whether or not an automatic brake control is active, and
whether or not an urgent brake operation has been performed. When
the automatic brake control is active or the urgent brake operation
has been performed, the drive starting and terminating timings are
set in order that the accumulator pressure is within the pressure
range B. It is to be noted that in each of such cases the driving
current (the driving duty) of the electric motor M is set to the
maximum (100%).
[0034] In accordance with the driving condition setting means DC of
the disclosed embodiment, a judgment is also made concerning
whether or not a brake fade occurs based on the detection result of
the pressure sensor PS2 and the wheel speed detected by the wheel
speed sensor WS. If it is judged that the brake fade occurs, the
drive starting and terminating timings are set in order that the
accumulator hydraulic pressure is within the pressure range B in
FIG. 2, as will be described in more detail below. Of course,
instead of the pressure sensor PS2, the stroke sensor BS can be
used to detect the brake fade.
[0035] When the vehicle load is small, or when the automatic brake
control is inactive, or when the vehicle is not in the urgent brake
operation but is in the normal brake operation, or when the brake
fade does not occur, the drive starting and terminating timings are
set in order that the accumulator hydraulic pressure is within the
pressure range A in FIG. 2.
[0036] As shown in FIG. 1, the pressure generator PG includes a
master cylinder MC and a hydraulic pressure booster HB which
assists the operation of the master cylinder MC by using the power
hydraulic pressure outputted from the auxiliary hydraulic pressure
source AP. The pressure generator PG further can be provided with
the pressure sensor PS2 which continuously detects the hydraulic
pressure outputted by the master cylinder MC. The output signal of
the pressure sensor PS2 (i.e., the detected result) is available or
can be sued for checking whether or not the automatic brake control
is active, or whether or not the vehicle is under the urgent brake
operation.
[0037] The aforementioned driving condition setting means DC, for
example, is constructed in an electronic control device CT as shown
in FIG. 3. The electronic control device CT is connected with the
pressure sensor PSI and other sensors, and controls the electric
motor M. As shown in FIG. 3, the electronic control device CT is
provided with a microcomputer CM formed by electronic devices, a
CPU, a ROM, a RAM, an input interface IT and an output interface OT
which are constructed to be mutually connected by way of buses. The
output signals of the aforementioned pressure sensor PS1 and others
are fed from the input interface IT to the CPU by way of an
amplifier circuit Al. A control signal is outputted from the output
interface OT to the electric motor M by way of a driving circuit
AO. In the micro computer CM, the ROM stores a program
corresponding to the flowchart shown in FIG. 4, the CPU executes
the program while an ignition key (not shown) is being turned on,
and the RAM temporally stores variables required for executing the
program.
[0038] In the above hydraulic brake system, the electronic control
device CT performs a series of operations for effecting the driving
control of the hydraulic pump FP, and the microcomputer CM begins
to execute the program immediately when the ignition key (not
shown) is turned on. Hereinafter, the procedure for the driving
control of the hydraulic pump FP will be described with reference
to the flowchart in FIG. 4. The drive starting and terminating of
the hydraulic pump FP and the controlling of the accumulator
hydraulic pressure are as described above and so a flowchart
illustrating such characteristics is not included.
[0039] First, at step 101 the microcomputer CM is initialized to
clear all the variables stored therein. Next, at step 102 the
output signals from the wheel speed sensor WS and other sensors are
fed into the microcomputer CM. Then the program proceeds to step
103 where the hydraulic pump FP is driven to output a low power
hydraulic pressure, whereby the electric motor M is driven or
operated so that the accumulator hydraulic pressure is within the
pressure range A in FIG. 2. At step 104, the CPU judges whether or
not the vehicle is stopped. When the CPU judges that the vehicle is
stopped, the program proceeds to step 105, and the hydraulic pump
FP is driven to output a very low power hydraulic pressure, whereby
the electric motor M is driven or operated so that the accumulator
hydraulic pressure is within the pressure range C in FIG. 2. Thus
electric power consumed by the electric motor M is reduced to
improve energy efficiency, thus improving the durability of the
hydraulic pump FP and the hydraulic pressure booster HB. Also, the
sound generated while the electric motor M is driven in this manner
is relatively small and so the noise associated with the overall
hydraulic pump is reduced.
[0040] At step 104, when the CPU judges that the vehicle is
running, the program proceeds to step 106 and the subsequent steps
to check whether or not the conditions for driving the hydraulic
pump FP to output a very high power hydraulic pressure are
satisfied. First, at step 106, the vehicle load is estimated based
on the output signal from the vehicle height sensor HS, and is
compared to a predetermined value Kw. If the vehicle load is found
to be equal to or greater than the predetermined value Kw, the
program proceeds to step 110 to drive the hydraulic pump FP to
output the high power hydraulic pressure. In this situation, the
electric motor M is controlled so that the accumulator hydraulic
pressure is within the pressure range B in FIG. 2. If the vehicle
load is found to be less than the predetermined value Kw, the
program proceeds to step 107.
[0041] At step 107, the CPU judges whether or not the automatic
brake control is active. More specifically, the electronic control
device CT determines whether or not automatic brake control such as
traction control, braking steering control, or inter-vehicle
distance control is necessary based on an operating condition of
the vehicle. When the electronic control device CT judges that the
automatic brake control is necessary, an automatic brake control
flag is set. The automatic brake control is deemed to be active
when the automatic brake control flag is set. Alternatively, the
automatic brake control can be deemed to be active when the brake
pedal is not found to be depressed based on the output signal from
a brake switch or the stroke sensor BS, or when the hydraulic
pressure is found to be supplied by the master cylinder MC based on
the output signal from the pressure sensor PS2, or when the
accumulator hydraulic pressure is found to be beyond the
predetermined value based on the output signal from the pressure
sensor PSI.
[0042] At step 107, when the CPU judges that the automatic brake
control is active, the program proceeds to step 110 to drive the
hydraulic pump FP to output the high hydraulic pressure. If the CPU
judges that the automatic brake control is inactive, the program
proceeds to step 108 to check whether or not the urgent or sudden
brake operation is done or completed. Here, the differential value
of the stroke detected by the stroke sensor BS (or the differential
value of the hydraulic pressure in the master cylinder MC detected
by the pressure sensor PS2) is determined, whereupon it is judged
whether or not the differential value is beyond a predetermined
reference value. When the differential value is beyond the
predetermined reference value, the urgent brake operation is found
to be done or completed, whereby the program proceeds to step 110
to drive the hydraulic pump FP to output the hydraulic pressure
high.
[0043] When the urgent brake operation is not found to be done, the
program proceeds to step 109 to check whether or not the brake fade
occurs. When the CPU judges that the brake fade occurs, the program
proceeds to step 110 to drive the hydraulic pump to output the high
hydraulic pressure. When the brake fade is deemed to not be
occurring, the program returns to step 104. Thus, the program
utilized in this described and illustrated embodiment is
constructed to proceed to step 110 when the condition specified in
any one of the steps 106-109 is satisfied. Alternatively, the
program can be constructed to go step 110 when some conditions of
all steps 106-109 are satisfied or when a combination of conditions
of any of steps 106-109 is satisfied.
[0044] At step 109, it is determined whether or not the brake fade
occurs as described below. The friction coefficient of a brake pad
becomes gradually smaller as the friction surface of the brake pad
becomes heated through repeated braking operation. In such a case,
it is desirable to increase the braking force. However, it may be
difficult to detect whether or not the brake fade occurs. When the
brake fade occurs, the braking force (i.e., deceleration) drops or
is reduced as shown by the two-dotted line in FIG. 5 which is
positioned below the solid line representing the normal braking
force. Even if the braking force drops or is reduced, it may not be
possible to estimate that the brake fade occurs.
[0045] In view of this, in the present embodiment, by continuously
detecting how the braking force relative to the brake pedal input
force changes, the brake fade occurrence zone can be defined as
noted by the area enclosed by the one-dotted lines in FIG. 6. It is
to be noted that the solid line in FIG. 6 indicates the
characteristics when the braking operation is normal and the
two-dotted line in FIG. 6 indicates the characteristics when the
auxiliary hydraulic pressure source AP is in failure.
[0046] As shown in FIG. 1, the driving condition setting means DC
is constructed to judge whether or not the brake fade occurs based
on both the detected result from the pressure sensor PS2 and the
speed detected by the wheel speed sensor WS. More specifically, an
estimated vehicle body speed is first calculated based on the wheel
speed detected by the wheel speed sensor WS. Next, a vehicle body
acceleration (which includes a vehicle body deceleration) is
calculated by differentiating the vehicle body speed. A
relationship between the vehicle body acceleration and the brake
pedal input force speed, which is detected by the pressure sensor
PS2, is represented by a map, in which the brake fade occurrence
zone is defined. The brake pedal input force can be replaced with,
for example, a detected signal from a depression sensor or the
pedal stroke which is represented by the detected signal from the
stroke sensor BS. If the brake fade is deemed to occur, the driving
starting and terminating timings of the electric motor M are set in
order that the accumulator hydraulic pressure is within the
pressure range B in FIG. 2.
[0047] The principles, preferred embodiments and mode of operation
of the present invention have been described in the foregoing
specification. However, the invention which is intended to be
protected is not to be construed as limited to the particular
embodiments disclosed. Further, the embodiments described herein
are to be regarded as illustrative rather than restrictive.
Variations and changes may be made by others, and equivalents
employed, without departing from the spirit of the present
invention. Accordingly, it is expressly intended that all such
variations, changes and equivalents which fall within the spirit
and scope of the present invention as defined in the claims, be
embraced thereby.
* * * * *